They can refuse to recognize it as a valid license to drive a vehicle.

For nearly all purposes, Canadian and American driver licenses are acceptable in each other’s countries as valid ID and proof of proficient driving ability. Ontario can’t ask New York to suspend his license, but Canada can declare his license as invalid for driving purposes.

If you get a DUI in the US in your personal car and later try to drive professionally (class-B or class-A) into Canada, they will turn you away at the border and it’s a huge process to get them to waive the restriction. Doesn’t matter to them if your license is still valid in the US.